Using the European corn borer, Ostrinia nubilalis, as the principal experimental animal, this research program is devoted to the elucidation of the physiology of photoperiodic responses. The role of photoperiod in the determination of developmental pathways (diapause, nondiapause) will be studied from both experimental and theoretical standpoints. The formulation of a theoretical biological clocc underlying developmental determination will be given major emphasis. Studies will also be conducted to determine the role of a blood-brain barrier in the maintenance and termination of photoperiodically regulated diapause, and the metabolic characteristics associated with the diapause state.